1. Field of the Invention
The present invention relates to low fluid loss salt saturated cement slurries, additives and methods of use in oil and gas well cementing operations.
2. Description of the Prior Art
In oil and gas well primary cementing, a hydraulic cement slurry is pumped down a well bore penetrating a subterranean formation through a steel conduit disposed in the well bore and back up through the annulus between the conduit and the well bore. Upon setting, the cement bonds and supports the conduit within the well bore and prevents fluid movement between subterranean formations penetrated by the well bore. To be useful as an oil field cementing slurry, the cement slurry, among other things, must be capable of allowing adequate placement time before setting, have low viscosity while being pumped, resist fluid loss into subterranean formations, have low free water separation and have rapid short-term strength development.
In a number of primary cementing applications, the use of aqueous salt saturated cement slurries is advantageous. The salt, generally sodium chloride, functions as a dispersant in the slurry, and causes the slurry to expand upon setting whereby the attainment of a good bond between the well bore and casing upon setting of the slurry is enhanced. In addition, aqueous salt saturated cement slurries help prevent the swelling of clays and the sloughing of saltcontaining shale and other formations which in turn prevent problems such as bridging and lost circulation.
In remote or offshore locations where the availability of bulk blending equipment is limited, liquid fluid loss reducing additives for forming low fluid loss cement slurries are advantageous. Such liquid additives can be added directly to the water used to form the slurry without the need for special mixing equipment.
By the present invention, low fluid loss salt saturated cement slurries, liquid additives for use in forming such slurries and methods of using the slurries are provided.